This invention relates to a fuel injection injector controller for controlling a fuel injector for fueling an internal combustion engine.
Hitherto, a solenoid valve injector has been adopted as a fuel injection device into an internal combustion engine. A controller of the injector obtains information concerning the running state of an engine and calculates a fuel injection amount for setting the air fuel ratio of the internal combustion engine to a desired air fuel ratio based on the information according to the injector drive time. An electric current is supplied to the injector during the drive time. When the injector is energized, it opens its valve for injecting fuel and when the injector is de-energized, it closes its valve for stopping the fuel supply.
In such an injector, it is desirable to open the valve as soon as the injector is energized and close the valve as soon as the injector is de-energized in order to accurately match the calculated drive time and fuel injection amount. To enhance responsivity of the injector, a system is proposed, for example, as shown in Unexamined Japanese Patent Publication 1-318740.
In the system disclosed here, when energization of an injector is started, an excessive current called overexcitation current is supplied, thereby hastening the valve opening operation of the injector. After the valve is opened, the energization current is lowered to a holding current required for holding the valve of the injector open and the holding current is held for suppressing heat generation of the injector and decreasing a power loss. This is called overexcitation energization control.
Although the system supplies an overexcitation current when energization of the injector is started, the overexcitation current depends on battery voltage and if the battery voltage is low, the overexcitation current value also lessens and it is difficult to sufficiently hasten the valve opening operation.
When the valve of the injector is closed, the conventional injector controller relies only on high-speed shutdown for an LCR resonance circuit to consume energy accumulated in an excitation circuit of the injector; it is difficult to sufficiently hasten the valve opening operation.
Thus, to control an injector for such high-speed response application controlling a high fuel pressure, such as an injector for cylinder injection of fuel into a gasoline engine or a fuel injection injector into a diesel engine, the controller is not sufficient in the aspect of control responsivity or control resolution and it is difficult to sufficiently widen the injector control range.
To hold the valve open state in the injector, the conventional injector controller feeds back the energization current value of the injector, generates a triangular wave rising when the current value is smaller than a target value and falling when the current value is larger than the target value, and supplies the triangular wave as a holding current. However, the triangular wave depends on the battery voltage. More particularly, although the speed when the current value is lowered depends on factors other than the battery voltage, the speed when the current value is raised also depends on the battery voltage.
That is, if the battery voltage is low, sufficient power is not supplied and if an attempt is made to raise the current value, it takes time as compared with the case where the battery voltage is sufficiently high. Thus, if the battery voltage is low, the time until the triangular wave rises from the bottom to the top is prolonged. Resultantly, the ripple period of the triangular wave is prolonged.
Here, assume that the target value is the holding current value of the injector. If the ripple period is short, the injector cannot follow the triangular wave, thus the injector holds the valve open state. If the ripple period is prolonged, the injector follows the triangular wave and there is a possibility that the valve will be closed when the value is less than the holding current.
Thus, the target value needs to be set to a current value higher than the holding current value to set more than the holding current value even at the bottom of the triangular wave; power consumption is large.